sfxge(4): store licensing state in efx_lic

Check licensing support at NIC startup to avoid multiple checks later.
As state is stored, licensing initialisation is moved later in start
procedure.

Submitted by: Richard Houldsworth <rhouldsworth at solarflare.com>
Sponsored by: Solarflare Communications, Inc.
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D6385